Photocurable resins are of continuing interest because they are regarded as ‘green’ solutions, not requiring solvents nor, if containing water, energy intensive water drying resources. Within this area, it is of growing interest to provide photocurable resin compositions which after curing result in high toughness and increased thermal properties. Such desired properties are particularly sought in three dimensional printing applications.
For example, liquid-based Solid Imaging is a process whereby a photoformable liquid is coated into a thin layer upon a surface and exposed imagewise to actinic radiation, for example UV directed by laser for StereoLithography ‘SL’, such that the liquid solidifies imagewise. Subsequently, new thin layers of photoformable liquids are coated onto previous layers of liquid or previously solidified sections. The new layers are then exposed imagewise in order to solidify portions imagewise and in order to induce adhesion between portions of the new hardened region and portions of the previously hardened region. Each imagewise exposure is of a shape that relates to a pertinent cross-section of a photohardened object such that when all the layers have been coated and all the exposures have been completed, an integral photohardened object can be removed from the surrounding liquid composition.
One of the most important advantages of the solid imaging process is the ability to rapidly produce actual articles that have been designed by computer aided design. A significant amount of progress has been made with compositions and processes that have been adapted to improve the accuracy of the articles produced. Also, composition developers have made significant progress toward improving individual properties such as the tensile modulus or Heat Deflection Temperature (also called HDT being the temperature at which a sample of material deforms under a specified load) of the photohardened articles. Typically, a material with a higher HDT will perform better, that is, resist distortion better, in high-heat situations.
Rapid prototyping users wish to obtain quickly functional parts with good mechanical properties similar to those obtained by e.g.: injection molding or extrusion. Further it is desirable to produce parts with which, for examples, are achieved (1) high green strength which allows an easier handling of the parts at the end of the build and (2) outstanding toughness comparable to those of the acrylonitrile-butadiene-styrene “ABS” and polycarbonate thermoplastic polymers. These requirements are not only a customer request for rapid prototyping, but it is also, compulsory if SL or jetting resins are used for rapid manufacturing applications.
Additionally, it would be desirable to produce a clear photocurable composition which, for example, upon cure in a stereolithography process produces an article having the properties and feel of the manufacturing material acrylonitrile-butadiene-styrene (“ABS”) and polycarbonate (PC). Especially important for the laser based stereolithography process are formulations based on epoxy-acrylic resin mixtures. These formulations further require tougheners to produce balanced mechanical properties.
In EP1290088, it is disclosed that the addition of triblock copolymers having at least one block predominantly composed of methyl methacrylate units to epoxy compositions results in epoxy materials with improved impact resistance.
The patent application WO 03/063572 describes thermoset materials with improved impact strength, obtained from compositions comprising a hardenable resin, typically epoxy resin, a polyamide resulting from the condensation of at least one diacid and at least one diamine, and possibly an impact modifier selected from SBM, BM and MBM copolymers.
There is a general need in improving the properties of the cured resins as such used for stereolithography and the products made thereof, as well as the initial storage properties of the uncured composition and in the intermediate green model and the final cured product. The green model is an object of a well-defined shape obtained by iterative layer depositions and irradiations. The green model is, in general, not fully cured and has a lower strength (greenstrength) than the final part, and must therefore be submitted to a post-curing process.
It is therefore an object of the present invention to provide a resin composition suitable for the use in photocurable coatings per se, and in specific for stereolithography and other such three dimensional printing applications where a 3D object is formed, showing improved properties compared to those of the state of art. It is a further object to improve the impact resistance of the cure article in accordance with the specific requirements.